The issue of Russian military personnel going absent without leave is believed to have got worse after last year's draft.
The number of Russians escaping from the army has lept, according to the British Ministry of Defence (MoD).
Citing "credible research by independent Russian journalists", they said there were 1,053 cases in Russian military courts of people going AWOL between January and May 2023 - more than during the whole of 2022.
"Russia's military has struggled to enforce discipline in its ranks throughout its operations in Ukraine," it wrote in a daily intelligence briefing on Wednesday, adding the "forced mobilisation of reservists" had "highly likely worsened" the issue.
Moscow ordered a "partial mobilisation" last September, drafting in around 300,000 people to serve in the armed forces.
The move triggered protests across the country, amid reports poorer or ethnic minority populations were being disproportionately called up.
In its intelligence briefing, the British MoD said "most of those found guilty of going AWOL are now punished with suspended sentences, meaning they can be redeployed to the special military operation."
"Russia's efforts to improve discipline have focused on making examples... and promoting patriotic zeal, rather than addressing the root cause of soldiers' disillusionment," it added.
Russian deserters - including Wagner mercenaries - have allegedly been executed in Ukraine, with a Euronews report finding Chechen fighters were being used to enforce discipline on disgruntled troops.
Multiple reports from Ukraine also exist of Russian conscripts being detained - at times, locked in cellars or basements - for refusing to fight.
Russian soldiers have been widely documented as facing appalling conditions, enduring the cold, hunger and abuse from commanders.
Meanwhile, many newly mobilised troops have complained about being sent to a war zone without sufficient equipment or training.
Assessing whether Russians want to fight is a complex issue.
On the one hand, some observers insist an unpopular invasion has been forced upon relatively powerless ordinary Russians, with the authorities clamping down hard on dissent. On the other, there are claims the war would not be possible without broad popular support.
An investigation by the BBC’s Russian service showed that Russia’s defence ministry offered lucrative short-term contracts to people with no combat experience to join the army.
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